David Deutsch’s “The Beginning of Infinity” Chapter 11 “The Multiverse” Part 4, ToKCast Episode 27

00:00:19.600 Hello and welcome to episode 27 of Topcast. I say 27 on YouTube it's episode 27 but if you go to
00:00:27.840 iTunes or if you go to Podbean or one of those other places where the audio only versions of
00:00:33.920 these podcasts come out you'll find the numbering are slightly different there are more audio only
00:00:39.200 versions of Topcast and what there are video versions all of the beginning of Infinity
00:00:43.600 material is definitely on YouTube however. Okay so we're still on chapter 11 this is the
00:00:49.040 multiverse it's part 4 now of the multiverse and I'm anticipating today that we'll finish the
00:00:54.800 multiverse so I'm going to be sticking reasonably closely to the book today but also at the end
00:01:00.480 we're going to do a little bit of a short story and the purpose of the short story is to emphasize
00:01:05.520 exactly how the multiverse is indeed a testable theory and testable against other ways of looking at
00:01:12.400 quantum theory that have been tried over the years the other so-called interpretations so we tend
00:01:19.200 not to call the multiverse an interpretation of quantum theory we tend to just call it quantum theory
00:01:25.760 in the same way that dinosaurs are just how we explain what fossils are we tend not to add on this
00:01:32.400 whole idea of dinosaurs are in our interpretation of fossils even though they are but they are the
00:01:38.800 only interpretation of fossils they're the only scientific interpretation of fossils and in the
00:01:43.920 same way if we take quantum theory literally we are kind of forced into this idea of the multiverse
00:01:50.480 because it is a simply a literal reading of what the equations are saying in particular I'd like
00:01:56.080 to refer to the Schrodinger wave equation so the Schrodinger wave equation describes all the
00:02:01.120 for example positions in which an electron can occupy around a nucleus and there's a variety of them
00:02:08.240 simultaneously and so taking that literally means that the electron really is in these different
00:02:13.600 positions now not in the one universe that's not possible but in although there is a sense in which
00:02:18.880 the electron is spread out around the nucleus as we've talked about before it has this kind of
00:02:24.640 ink block character as David describes at the beginning of infinity but more than that it extends
00:02:30.480 across many universes occupying all physically possible places across the multiverse around that
00:02:38.400 nucleus but let's go back to the book now recapping what's been said in previous episodes
00:02:45.280 we've been talking about this story where there are people on a spaceship that has a
00:02:50.000 transporter and the transporter malfunctions and in one spaceship the transporter malfunction
00:02:55.200 causes a spark which causes a person to spill some coffee which then causes them to have an
00:02:59.840 interaction with another person which leads to romance and so on and in the other universe there
00:03:05.200 is no such spark there is no transporter malfunction so we have this differentiation of the
00:03:09.760 universes that prior to which prior to which the spark or malfunction happened we had fungible
00:03:15.280 universes we had two universes but they are absolutely identical in all respects and then this
00:03:20.960 deterministic law this deterministic event causes the universes to differentiate and we had a
00:03:28.640 story going on so far about that it's a fictional story you diving straight back into the beginning
00:03:34.960 of infinity David writes in the real multiverse there is no need for the transporter or any other
00:03:41.120 special apparatus to cause histories to differentiate and to rejoin under the laws of quantum physics
00:03:47.040 elementary particles are undergoing such processes of their own accord all the time moreover
00:03:53.120 histories may split into more than two often into many trillions each characterized by a slightly
00:03:58.880 different direction of motion or difference in other physical variables the elementary particle
00:04:03.280 concerned also in general the resulting histories have unequal measures so let us now
00:04:09.440 dispense with the transporter in the fictional multiverse too let's pause their my reflection
00:04:14.640 so only in very contrived quantum experiments might we get equal measures by which we mean 50 50
00:04:21.280 so let's say for example we have a photon heading towards a half silver mirror now we can
00:04:27.120 contrive the experiment there such that half of the instances of the electron go straight through
00:04:32.480 and half of the electrons instances get reflected off that's where we have equal measures that's
00:04:38.000 all measure means it's kind of like a proportion however in general this is not what happens
00:04:43.600 when an electron or when a subatomic particle in elementary particle has a choice about what to do
00:04:49.440 I say choice of course it doesn't have conscious choice when there is a possibility of it going one
00:04:54.800 way rather than another it typically isn't 50 50 the measure of universes is some other proportion
00:05:01.040 you know it could be spread amongst 10 20 30 as long as they all add up to 100 in the end
00:05:07.600 it could be any percentage that you like and when I say any percentage that you like of
00:05:11.920 course I mean any percentage as determined by the physical laws that are governing that particular
00:05:16.720 event at that particular time let's go back to the book the rate of growth in the number of
00:05:22.240 distinct histories is quite mind boggling even though thanks to interference there is now a
00:05:26.480 certain amount of spontaneous rejoining as well because of this rejoining the flow of information
00:05:32.080 in the real multiverse is not divided into strictly autonomous subplers branching autonomous
00:05:36.880 histories although there is still no communication between histories in the sense of message
00:05:41.680 sending they are intimately affecting each other because the effective interference on a history
00:05:46.960 depends on what other histories are present not only is the multiverse no longer perfectly
00:05:53.200 partitioned into histories individual particles are not perfectly partitioned into instances
00:05:58.640 for example consider the following interference phenomenon where x and y now represent different
00:06:03.440 values of the position of a single particle so we've got here x and y so that the particle could
00:06:09.760 be at either position x or at position y and then these histories join together so that the particle
00:06:16.320 is now at position x and then at some later time it differentiates again the universe differentiates
00:06:21.840 again such that the particle could now be in x or y once more and the blurb underneath that
00:06:29.440 picture says how instances of a particle lose their identity during interference has the
00:06:35.200 instance of the particle at x stated x or moved at y move to y as the instance of particle y
00:06:41.200 return to y or move to x and David's about to explain why this kind of question doesn't really
00:06:47.200 make any sense because fungibility completely erases in a sense the identity of which instances
00:06:52.400 which instance it doesn't make any sense to ask the question let's persevere David right
00:06:58.240 because these two groups of instances of the particle initially at different positions have gone
00:07:02.960 through a moment of being fungible there is no such thing as which of them has ended up at which
00:07:07.840 final position this sort of interference is going on all the time even for a single particle in a
00:07:14.240 region of otherwise empty space so there is in general no such thing as the same instance of a
00:07:19.280 particle at different times okay just pause their my reflection this is just like with the finance
00:07:26.080 example we had right at the beginning of the chapter if there's two dollars in your bank account
00:07:30.960 and the tax office owns one of them it makes no sense to say which of them is yours and which
00:07:36.480 of them is the tax office all we know is that one of them belongs to your one belongs to tax office
00:07:41.200 but they're fungible even though there are two there's diversity within fungibility there's a
00:07:45.360 difference between them however we can't say which of them belongs to so our usual way of speaking
00:07:51.920 our language is sort of reached its limits when we start talking about these things like the
00:07:56.880 multiverse right at the edge of our understanding of science and I'll just emphasize now as well
00:08:04.160 the astonishing fact that you yourself are made up of uncountably infinite numbers of instances of
00:08:11.520 yourself possibly uncountably infinite number if it's not uncountably infinitely large then it's
00:08:16.320 certainly a very large number of instances of yourself occupy the space and time where you are now
00:08:23.120 that's very strange you might think what does it mean for me to be made up of many many instances
00:08:28.800 of myself well it doesn't mean anything over and above what you thought of your self identity prior
00:08:34.400 to knowing this when something happens where you actually physically differentiate into two
00:08:42.640 versions of yourself where you could have gone left or right and you ended up going left
00:08:49.200 and copies of you went to the right you're no longer one of those copies that went to the right
00:08:56.080 you're only the instances that went to the left all those instances that went to the right
00:09:00.640 they're no longer you in a sense they're copies of you I would say all the copies that went to
00:09:05.520 left will dare you and so you feel the way you feel having gone to the left and you will never know
00:09:11.280 what it was like to have gone to the right or what happens to that person it's like the sliding doors
00:09:15.280 movie so what I would say about personal identity is then is that they are now two versions of you
00:09:21.440 but you are you and you are different too the copy that just went to the right you are only the
00:09:26.080 copies that went to the left and that continues to happen they continues to be this branching if you
00:09:30.400 like this branching of not only elementary particles but everything in the physical universe does
00:09:36.800 this as well again amazing astonishing but not unbelievable I'm not unbelievable okay let's go back to
00:09:45.120 the book even within the same history particles in general do not retain their identities over time
00:09:51.120 for example during a collision between two atoms history is the event split into something like this
00:09:57.120 so either we can have the two atoms that apparently collide collide such that one retains its
00:10:04.160 identity another retains its identity having bounced off one another that's what that first
00:10:08.480 diagram is showing or something like that which is where the two particles pass through each other
00:10:12.800 in either case they retain their identities and David writes so for each particle individually
00:10:18.640 the event is rather like a collision with a semi-sovered mirror each atom plays the role of the mirror
00:10:23.280 for the other atom but the multi-versal view of both particles looks like this where at the end of
00:10:30.160 the collision some of the instances of each atom have become fungible with what was originally
00:10:34.960 a different atom of course they're just my reflection what I was saying before about a human being
00:10:42.880 okay this happens for everything okay it doesn't just happen for human being as it happens for
00:10:48.480 any living thing cats and dogs and happens for planets it happens for anything that you like
00:10:52.560 where something could have happened one way but in fact happens a different way although that
00:10:57.600 differentiation can happen so far as I know it's not possible for anything much larger than
00:11:02.880 elementary particles perhaps atoms okay fine but nothing like a human being can then interfere with
00:11:09.680 itself it's not like the two instances of you one having gone one set of instances having gone
00:11:16.080 left and one set of instances having turned right will then recombine and interfere I don't think
00:11:21.520 that's physically possible back to the book for the same reason there is no such thing as the
00:11:26.480 speed of one instance of a particle at a given location speed is defined as distance divided by time
00:11:32.000 taken but that is not meaningful in situations where there's no such thing as a particular instance
00:11:36.720 of the particle over time instead a collection of fungible instances of a particle in general
00:11:43.280 have several speeds meaning that in general they will do different things in instant later this is
00:11:49.200 another instance of diversity within fungibility not only can a fungible collection with the same
00:11:54.800 position have different speeds a fungible group with the same speed can have different positions
00:11:59.200 furthermore it follows from the loss of quantum physics that for any fungible collection of
00:12:03.680 instances of a physical object some of their attributes must be diverse this is known as the
00:12:09.200 Heisenberg uncertainty principle after the physicist Werner Heisenberg who deduced the earliest
00:12:15.360 version from quantum theory pause their my reflection emphasizing the word deduced there so this
00:12:22.560 is not a an axiom or a postulate of quantum theory it is derived from quantum theory from
00:12:30.240 more basic things it is a consequence of the rest of quantum theory that is what the uncertainty
00:12:36.240 principle is about so poorly named as David will explain shortly but it just means that for any
00:12:44.000 instance or for any elementary particle let's say let's stick with elementary particle like an
00:12:49.120 electron it doesn't have a super sharp position it's not in a particular place at any given time
00:12:56.720 it is spread out in space like an ink blot so too is it speed and so in fact the way that the
00:13:07.200 the way that Heisenberg's uncertainty principle works is that the sharper that you try to make
00:13:11.920 your the position of your electron then the less sharp things like the speed of the electron become
00:13:21.760 now for anyone who has studied classical physics you don't even need quantum physics for that
00:13:27.040 you will understand something called diffraction perhaps okay diffraction of light this is where
00:13:31.680 you narrow a slit through which light can pass and the more and more narrow you make the slit
00:13:38.240 the more that the light going through the slit spreads out it diffracts more and more this is
00:13:45.200 certainly related to quantum theory but to a first approximation we can simply talk about the fact
00:13:49.920 that we are isolating the photons that pass through the slit to a particular point in space
00:13:54.880 we've narrowed the x value and by narrowing that x value the delta x value the possible
00:14:01.280 positions where it can be what we make uncertain is all the different ways in which it can have
00:14:07.280 momentum it can have speed and so it could go more to the left and more to the right so the
00:14:14.800 uncertainty principle actually kind of predates quantum theory in a certain sense there's a
00:14:20.640 version in classical theory just to do with diffraction simple classical diffraction back to the book
00:14:27.440 David Wright hence for instance an individual electron always has a range of different locations
00:14:33.120 and a range of different speeds and different directions of motion as a result it's typical
00:14:39.440 behavior is to spread out gradually in space it's quantum mechanical law of motion resembles the
00:14:44.800 law governing the spread of an ink blot so if it is initially located in a very small region
00:14:50.880 it spreads out rapidly and the larger it gets the more slowly it spreads the entanglement
00:14:56.320 information that it carries ensures that no two instances of it can ever contribute to the same
00:15:01.600 history or more precisely at times and places where there are histories it exists in instances
00:15:06.880 which can never collide if a particle's range of speeds is centered not on zero but on some
00:15:12.320 other value then the whole of the ink blot moves with its center obeying approximately the laws
00:15:18.640 of motion in classical physics in quantum physics this is how motion in general works
00:15:25.120 skipping a short bit and then David writes now put a proton into the middle of that gradually
00:15:30.720 spreading cloud of instances of a single electron the proton has a positive charge which attracts
00:15:36.480 the negatively charged electron as a result the cloud stops spreading when when it size is such that
00:15:42.320 tendency to spread outwards due to its uncertainty principle diversity is exactly balanced by its
00:15:48.400 attraction to the proton the resulting structure is called an atom of hydrogen historically
00:15:54.960 this explanation of what atoms are was one of the first triumphs of quantum theory
00:15:59.520 for atoms could not exist at all according to classical physics okay pause there just my
00:16:04.080 reflection I'm reason why classically atoms shouldn't exist is because in classical physics
00:16:09.280 we knew that for example accelerating electrons in a magnetic field causes electromagnetic
00:16:15.760 radiation to be produced and so this is how radio works for example right so a radio a radio
00:16:22.240 transmitter radio transmitter will literally radio transmitter is like just a piece of metal right
00:16:27.440 it's a it's an aerial it's a wire and what you do is you accelerate an electron up and down
00:16:32.880 that aerial up and down the wire or antenna I think sometimes it's called anyway the transmitter
00:16:38.160 is a piece of wire and the faster that the electron goes up and down there then the higher
00:16:44.240 the frequency of the radiation that escapes from there but you have to keep on providing energy
00:16:49.440 in order for the electron to go up and down so that you can produce more and more photons
00:16:54.080 of light coming out okay radio photons if you want to create radio waves okay and so this is the
00:16:58.720 principle of how radio's operate electrons vibrate up and down a piece of metal of some sort okay
00:17:04.160 it doesn't have to be metal these days and the mobile phone it's not necessarily metal
00:17:06.960 I mean it's a carbon area or something whatever the case energy is provided to the electrons
00:17:12.080 making them go up and down and that creates electromagnetic radiation now if you don't keep on adding
00:17:18.320 energy to this system to the transmitter then of course the radiation will stop the electrons will
00:17:24.800 stop moving what has this got to do with atoms well if an atom is really an electron going around
00:17:32.320 a proton then it's the same idea as the aerial the electron should be emitting photons of
00:17:38.800 radiation of some sort but in general they don't okay except under very special circumstances
00:17:44.960 the electron is going around but not emitting a radiation but it should be emitting radiation
00:17:49.600 and especially because the electron is moving in a circle so it's changing its direction while
00:17:54.560 moving in a surface moving in a sphere something like that it's going around anyway in order for it
00:17:58.880 to go around you know curved path that means it's changing its direction if it's changing its
00:18:04.400 direction there must be some energy causing it to change its direction okay a force has to be
00:18:08.800 applied and if there is no external source of energy doing this causing it to change its direction
00:18:13.840 then there must be an internal source of energy causing it to do that which should cause it to decay
00:18:18.640 into the orbit to decay into the nucleus so all atoms should have collapsed on the classical theory
00:18:26.720 but they don't so let's just read what David has to say about this
00:18:34.160 to he writes it used to be a mystery why electrons do not fall onto the nucleus in a flash of
00:18:39.760 radiation neither the nucleus nor the electrons individually have more than 110 thousandth the
00:18:45.040 diameter of the atom so what keeps them so far apart and what makes atoms stable at that size
00:18:51.120 in non-technical accounts the structure of atoms is sometimes explained by an algae with the solar
00:18:54.960 system one imagines electrons in orbit around the nucleus like planets around the sun
00:18:59.680 but that does not match the reality for one thing gravitationally bound objects do slowly spiral
00:19:04.240 in emitting gravitational radiation the process has been observed for binary neutron stars and the
00:19:09.760 corresponding electromagnetic process in an atom would be over in a fraction of a second for another
00:19:16.080 the existence of solid matter which consists of atoms packed closer together is evidence that
00:19:21.200 atoms cannot easily penetrate each other yet solar system certainly could furthermore it turns
00:19:26.640 out that in hydrogen atom the electron in its lowest energy state is not orbiting at all but as I
00:19:32.720 said just sitting there like an ink plot it's uncertainty principle tendency to spread out
00:19:38.240 exactly balanced by the electrostatic force in this way the phenomena of interference and diversity
00:19:44.000 within fungibility are integral to the structure and stability of all static objects including
00:19:49.040 all solid body bodies just as they are integral to all motion so pause there my reflection here
00:19:56.160 just to drive that point home if the classical version of the atom was true and we had this
00:20:05.840 electron orbiting the nucleus then indeed the atom would be almost entirely empty space and if
00:20:13.680 the atom was entirely empty space then atoms should go through each other and no matter would
00:20:18.880 really be solid because you have this single little electron orbiting this tiny little nucleus
00:20:23.680 and when you sit on a chair you should just go through the chair and worsen that you and the chair
00:20:27.760 should go straight through to the core of the earth etc okay this should be no solid matter to
00:20:32.640 begin with if the classical version of the atom was true but the classical version of the atom is
00:20:37.040 not true in fact what's going on is the atom is a multiverse object and so there are many many
00:20:44.720 instances of the electron and because there are many instances of the electron spread around the
00:20:49.920 nucleus like an ink blot then you can't have one atom penetrating another atom very easily that's
00:20:56.560 extremely difficult happens in certain circumstances when you get into neutron stars and the
00:21:01.600 weed areas of astrophysics and whatever putting outside that's situations where the gravitational force
00:21:06.880 actually overcomes the electrostatic force but this tendency to spread out means that the negative
00:21:13.680 cloud of any given atom such as the chair on which you sit the atoms on the chair in which you sit
00:21:20.800 and the reason that you know you can't push one hand through the other hand no matter how hard
00:21:25.200 you push is because the atoms in one hand contain electrons which are spread out around the atom
00:21:33.280 kind of like a cloud but better to say like this all the fungible many many of the fungible
00:21:40.400 instances are spread out all around the nucleus and so to the atoms in this hand and so the
00:21:47.360 fungible instances here are repelling the fungible instances there and you can't get
00:21:51.600 matted to go through matter for that reason back to the book the term uncertainty
00:21:57.920 principle is misleading let me stress that it has nothing to do with uncertainty or any other
00:22:03.520 distressing psychological sensations that the pioneers of quantum physics might have felt
00:22:08.160 when an electron has more than one speed or more than one position that has nothing to do with
00:22:14.000 anyone being uncertain what the speed is any more than anyone is uncertain which dollar in
00:22:19.360 their bank account belongs to the tax authority the diversity of attributes in both cases is a
00:22:24.640 physical fact independent of what anyone knows or feels nor by the way is the uncertainty principle
00:22:30.400 are principle for that suggests an independent postulate that could logically be dropped or
00:22:35.760 replaced to obtain a different theory in fact one could know more drop it from content theory
00:22:40.240 than one could admit eclipses from astronomy there is no principle of eclipses their existence
00:22:45.840 can be deduced from theories of much greater generality such as those of the solar systems geometry
00:22:51.760 and dynamics similarly the uncertainty principle is deduced from the principles of quantum theory
00:22:58.080 thanks to the strong internal interference that it is continuously undergoing a typical electron
00:23:03.280 is an irreducibly multiversal object and not a collection of parallel universal parallel
00:23:09.440 histories objects that is to say it has multiple positions and multiple speeds without being
00:23:13.360 divisible into autonomous sub entities each of which has one speed and one position even
00:23:19.040 different electrons do not have completely separate identities so the reality is an electron
00:23:23.680 field throughout the whole of space and disturbance has spread through this field as waves
00:23:29.680 at the speed of light or below this is what gave rise to the often quoted misconception among
00:23:36.320 look pioneers of quantum theory that electrons and likewise other particles are particles and waves
00:23:41.920 at the same time there is a field or waves in the multiverse for every individual particle that
00:23:48.480 we observe in a particular universe pause their my reflection this can be very difficult to
00:23:53.440 understand so there is a strict sense in which wave particle duality is absolutely false
00:24:01.840 namely that within any given universe like the one you occupy the electron is like this ink
00:24:09.520 lotting I prefer to regard it as more closely related to our concept of particle than anything
00:24:16.560 else one it's not is a wave the electron can't both be isolated at a single point and spread
00:24:25.520 out throughout all of space at the same time the wave function of an electron would suggest that
00:24:32.320 it is spread out greatly throughout a vast region of space that's what the wave function says
00:24:41.600 and that's what the wave model of the electron would also suggest as well if we were going to go
00:24:47.280 down that path in regard electrons as waves the electron is acts far more like a particle okay in
00:24:54.640 the experiments that can be done like the photoelectric effect showed the electron is in fact
00:24:59.760 far more particle like now that's one thing the other thing is that the multiverse exists
00:25:06.560 and if you could have a god's eye view of the multiverse then you would see that the
00:25:11.120 electron for example to pick one particle occupies all the physically possible places that
00:25:16.720 the electron could occupy given its wave function and that would look like a wave across the
00:25:21.760 entire multiverse across all the universes any person in a particular universe can't have access
00:25:28.320 to all those other universes can't observe those other universes but someone who was in theory
00:25:33.920 like a god outside of the multiverse I'm looking down at subatomic particles would see that they're
00:25:40.400 in all these different positions and that that multiverse a object which is the subatomic particle
00:25:46.800 or the electron would resemble a wave all of its positions would seem to be a wave because it would be
00:25:53.200 this continuously changing varying thing sometimes commonly in this place less commonly in that place
00:26:01.200 pick up peaks and troughs and so it would look like a wave the the and why in which you would
00:26:05.600 see all the different positions of the electron would resemble something like a wave okay now I'm
00:26:10.960 skipping another paragraph here and then David writes a history is part of the multiverse in the
00:26:17.360 same sense that a geological stratum is part of the Earth's crust one history is distinguished
00:26:22.480 from the others by the values of physical variables just as stratum is distinguished from others by
00:26:27.040 its chemical composition and by the types of fossils found in it and so on a stratum and a history
00:26:32.720 are both channels of information flow they preserve information because although their contents
00:26:37.200 change over time they are approximately autonomous that is to say the changes in a particular
00:26:41.760 stratum or history depend on most entirely on conditions inside it and not elsewhere it is because
00:26:47.040 of that autonomy but a fossil found today can be used as evidence of what was present when that
00:26:52.160 stratum was formed similarly it is why within a history using classical physics one can successfully
00:26:57.680 predict some aspects of the future of that history from its past a stratum like a history has
00:27:03.040 no separate existence over and above the objects in it it consists of them nor does the stratum
00:27:09.200 have a well-defined edges also there are regions of the earth for instance near volcanoes where
00:27:14.640 strata have merged although I think there are no geological processes that split and reemerge
00:27:19.360 strata in the way the history split and reemerge there are regions of earth such as the core
00:27:24.080 where there are never being strata and there are regions such as the atmosphere where strata do form
00:27:28.400 but their content interact and mix on much shorter time scales than in the crust similarly
00:27:32.960 there are regions the multiverse that contain short lived histories and others that do not
00:27:37.120 even approximately contain histories however there is one big difference between the ways in which
00:27:41.840 strata and histories emerge from their respective underlying phenomena although not every
00:27:46.960 atom in the earth's crust can be unambiguously assigned to a particular stratum most of the atoms
00:27:51.440 that form a stratum can and contrast every atom in an everyday object is a multiverse object
00:27:56.640 not partitioned into nearly autonomous instances and nearly autonomous histories yet every
00:28:01.280 area yet everyday objects such as star ships and betrothed couples which are made of such particles
00:28:06.800 are petitioned very accurately into nearly autonomous histories with exactly one instance one
00:28:12.240 position one speed of each object in a history that is because of the suppression of interference
00:28:19.120 by entanglement as I explained interference almost always happens either very soon after splitting
00:28:25.840 or not at all that is why the larger and more complex and object or process is the less its
00:28:31.520 gross behavior is affected by interference at that coarse grained level of emergence
00:28:36.640 events in the multiverse consist of autonomous histories with each coarse grained history consisting
00:28:42.560 of a swald of many histories differing only in microscopic details but affecting each other's
00:28:47.760 growing interference spheres of differentiation tend to grow at nearly the speed of light
00:28:51.840 so on the scale of everyday life and above those coarse grained histories can justly be called
00:28:57.280 universes in the ordinary sense of the word each of them some what resembles the objects of
00:29:03.360 classical physics and they can usually be called parallel because they are nearly autonomous to
00:29:07.760 the inhabitants each looks like each looks very like a single universe would pause their
00:29:13.360 my reflection just recall when I was speaking earlier about how it's rather strange to think that
00:29:19.520 you yourself are made of many many fungible instances of yourself right now and when a choice is
00:29:24.880 made in the universe such as you could have gone left or right instances of you that have gone right
00:29:30.400 cease to be you where if you choose to go left instances of you that choose to go left are still you
00:29:37.120 until such time as there's another choice to make however we don't get interference
00:29:41.520 of human beings they don't come back together for the reasons that they've just
00:29:45.760 says here okay the larger and larger the object becomes the less and less it's going to be affected
00:29:50.960 by interference okay back to the book microscopic events which are accidentally amplified
00:29:58.800 to that coarse grained level like the voltage surge in our story a rare in any one coarse grained
00:30:04.560 history but common in the multiverse as a whole for example consider a single cosmic
00:30:10.560 ray particle traveling in the direction of earth from deep space that particle must be traveling in
00:30:15.840 a range of slightly different directions because because the uncertainty principle implies that
00:30:19.360 in the multiverse it must spread sideways like an ink block as it travels by the time it arrives
00:30:25.040 this ink block may well be wider than the width of the whole earth so most of it misses
00:30:31.200 and the rest strikes everywhere on the exposed surface remember this is just a single particle
00:30:36.720 which may consist of fungible instances the next thing that happens is that they cease to be
00:30:44.000 fungible splitting through their interaction with atoms at their point of arrival into a finite
00:30:50.400 by huge number of instances each of which is the origin of a separate history in each such
00:30:56.960 history there is an autonomous instance of the cosmic ray particle which will dissipate its energy
00:31:01.440 in creating a cosmic ray shower of electrically charged particles thus in different histories
00:31:07.360 such a shower will occur at different locations in some that shower will provide a conducting
00:31:12.160 path down which a lightning bolt will travel every atom on the surface of the earth will be struck
00:31:16.480 by such lightning in some history in other histories one of those cosmic ray particles will
00:31:21.920 struck a human cell damaging some already damaged DNA in such a way as to make the cell
00:31:25.840 cancerists some non negligible proportion of all cancers are caused in this way as a result there
00:31:31.120 exist histories in which any given person alive in our history at any time is killed soon
00:31:35.920 afterwards by cancer there exist other histories in which the course of a battle of war is
00:31:40.320 changed by such an event or by a lightning bolt at exactly the right place in time or by any
00:31:45.200 countless other unlikely random events this makes it highly plausible that there exist histories
00:31:51.840 in which events have played out more or less as alternative history stories such as
00:31:56.480 fatherland and roma atona in or which or in which events in your own life played out very
00:32:02.000 differently for better or worse the great deal of fiction is therefore close to a fact somewhere
00:32:07.360 in the multiverse but not all fiction for instance there are no histories in which my story is
00:32:12.240 the transport of malfunction of true because they require different laws of physics nor are
00:32:18.320 there histories in which the fundamental constants of nature such as the speed of light or the
00:32:22.560 charge on electron are different there is however a sensing which different laws of physics
00:32:27.440 appear to be true for a period of time in some histories because of a sequence of unlikely
00:32:34.480 accidents they may also be universities in which there are different laws of physics as required
00:32:39.280 and anthropic explanations are fine-chaining but as yet there are no viable theory there is no
00:32:43.920 viable theory of such a multiverse pause their my reflection this is certainly related to what I
00:32:50.480 said in the last episode if you recall about these things called Harry Potter universes places where
00:32:56.720 magic has appeared to have worked but not places where magic actually does work okay go back to
00:33:03.200 last episode for that one and David also mentions there these other kinds of multiverse multiverse
00:33:12.080 is where different physical laws might actually be true but they're not scientific theories for now
00:33:21.840 they are rather metaphysical theories which is fine they're very interesting and again in the
00:33:27.040 last episode and the one before that I think I mentioned these other kinds of multiverse
00:33:31.440 non quantum multiverses much larger sets or classes indeed of multiverses okay back to the book
00:33:40.240 and David writes some of my own research in physics has been concerned with the theory of quantum
00:33:46.960 computers please are computers in which the information carrying variables have been protected
00:33:51.760 by a variety of means from becoming entangled with their surroundings this allows a new mode of
00:33:57.600 computation in which the flow of information is not confined to a single history in one type of
00:34:03.040 quantum computation enormous numbers of different computation taking place simultaneously can
00:34:07.760 affect each other and hence contribute to the output of a computation this is known as quantum
00:34:12.000 parallelism in a typical quantum computation individual bits of information represented in physical
00:34:17.360 objects known as qubits quantum bits in which there is a large variety of physical implementations
00:34:23.440 but always with two essential features first each qubit has a variable that can take one of two
00:34:29.360 discrete values and second special measures are taken to protect the qubits from entanglement
00:34:34.320 such as cooling them to temperatures close to absolute zero a typical algorithm using quantum
00:34:39.520 parallelism begins by causing the information carrying variables in some of the qubits to acquire
00:34:45.200 both their values simultaneously consequently regarding those qubits as a register representing say
00:34:51.920 a number the number of separate instances of the register as a whole is exponentially large
00:34:57.520 two to the power of the number of qubits then for a period classical computations are performed
00:35:03.200 during which waves of differentiation spread to some of the other qubits but no further because of
00:35:08.640 the special measures because of the special measures to prevent this hence information is processed
00:35:14.160 separately in each of the vast numbers of autonomous histories finally and interference
00:35:20.720 process involving all the affected qubits combines the information in those histories into a single
00:35:26.160 history because of the intervening computation which has processed the information the final state
00:35:31.600 is not the same as the initial one as in the simple interference experiment I discussed
00:35:37.040 but it's some function of it like this okay and there's a picture or a representation of what's
00:35:43.600 going on where in a typical quantum computation you've got x splitting into all these different
00:35:51.040 possible histories okay all these different possible versions then interference happens and they
00:35:56.960 all combine together to give you the output function and David writes just as the Starship crew
00:36:03.760 members could achieve the effect of large amounts of computation by sharing information with their
00:36:07.520 doppelgangers computing the same function on different inputs so an algorithm that makes use
00:36:13.280 of quantum parallelism does the same but while the fictional effect is limited only by Starship
00:36:18.720 regulations that we may invent to suit the plot quantum computers are limited by the laws of physics
00:36:23.520 that govern quantum interference only certain types of parallel computation have been performed with
00:36:28.960 the help of the multiverse in this way they are the ones for which the mathematics of quantum
00:36:32.800 interference happens to be just right for combining into a single history the information that is
00:36:37.760 needed for the final result in such computations a quantum computer would only a few hundred cubits
00:36:43.120 could perform far more computations in parallel than there are atoms in the visible universe
00:36:48.560 at the time of writing quantum computers with about 10 cubits have been constructed
00:36:53.920 scaling the technology to larger numbers is a tremendous challenge for quantum technology
00:36:58.560 but it is gradually being met of course the MRI reflection so again as I've mentioned in previous
00:37:05.440 episodes once we've got fully functioning quantum computers of the kind David just described there
00:37:11.840 where the resources classically that would have been required to complete the computation would
00:37:19.840 exceed all of the atoms in the known visible universe we have to conclude that the computational
00:37:26.160 resources that are actually performing that computation successfully exist somewhere and it's not
00:37:31.440 in the visible universe hence the multiverse must exist so once we have that proof if you like
00:37:39.200 once we have that evidence or that problem the only known explanation of which is that the
00:37:44.560 universe and reality is much much greater than we ever thought then the majority of physicists
00:37:49.920 one would presume will be on board with the multiverse finally now as of today like David says
00:37:57.200 we've got quantum computers back then when the beginning of infinity was written of 10 cubits I don't
00:38:02.800 know what it is today it depends on who you ask which university you go to sometimes in quantum
00:38:09.600 computation now there is this issue but necessarily say problem there is this issue where the
00:38:17.440 results of what's going on aren't published kind of like with pharmacology where there is a
00:38:24.480 tension between commercial confidence and wanting to keep your intellectual property to yourself so
00:38:33.040 that your competitors don't have access the information you do so that's on the one hand you don't
00:38:37.520 want to publish all of your results about how good your quantum computation is or how good your
00:38:41.760 particular medicine is the tension between that and the usual process of peer review and getting
00:38:47.600 other scientists to be able to check your results to see that you haven't made errors so I literally
00:38:54.880 don't know what the best quantum computer is right now there are places where things are going
00:39:02.000 very well where they've got only four six cubits something like that but others are claiming they've
00:39:09.360 got you know hundreds of cubits and they're doing things but there's very few published results
00:39:14.800 and I'm not up on all that but I'm sure Google search will reveal more than what I can teach you
00:39:20.000 here now okay now I'm going to skip a significant part here and move on to something about
00:39:27.760 how discrete changes of energy can occur especially around an atom let's say for example where
00:39:35.200 an electron absorbs a photon when an electron absorbs a photon remember there are a few things
00:39:41.760 that could happen one thing that could happen is that nothing observable happens beyond the photon
00:39:50.080 striking the electron and then the photon disappearing and no apparent change in the electron occurring
00:39:55.760 or the photon strikes the electron orbiting the atom and the electron moves up an energy level
00:40:02.640 around the atom so it moves up to a higher orbital or indeed if the electron is struck by a photon
00:40:08.880 where it's sufficient energy it can knock the electron completely out of the atom altogether
00:40:14.080 but what we're interested in here is this idea of the quantum where where the electron absorbs
00:40:20.560 just the right amount of energy such that it moves from one particular energy level up to another
00:40:25.920 particular energy level and so the photon coming in is a single quantum of energy okay but
00:40:33.360 what David has to write about this particular phenomenon and he writes now let us look at the arrival
00:40:39.040 of that single quantum of energy to see how that discrete change can possibly happen without any
00:40:44.640 discontinuity consider the simplest possible case an atom absorbs a photon including all its energy
00:40:52.720 this energy transfer does not take place instantaneously forget anything that you may have read
00:40:57.680 about quantum jumps there are myths pause there just my reflection you can look at David's
00:41:03.360 edge question answer on what scientific idea needs to be retired and he said the idea of quantum
00:41:09.680 jumps and just google that quantum jumps David Deutsch and you'll find some really interesting
00:41:15.280 material there let's keep going David writes there are many ways in which it can happen but the
00:41:21.760 simplest is this at the beginning of the process the atom is in say its ground state in which
00:41:27.200 its electrons have the least possible energy allowed by quantum theory that means that all its
00:41:33.280 instances within the relevant course grain history have that energy assume that they are also
00:41:39.120 fungible at the end of the process all those instances are still fungible but now they are in
00:41:44.560 the excited state which has one additional quantum of energy what is that atom like halfway through
00:41:51.440 the process its instances are still fungible but now half of them are in the ground state and half
00:41:57.520 in the excited state it is as if a continuously variable amount of money changed ownership gradually
00:42:05.440 from one discrete owner to another this mechanism is ubiquitous in quantum physics and as the
00:42:11.280 general means by which transitions between discrete states happen in a continuous way in classical
00:42:17.040 physics a tiny effect always means a tiny change in some measurable quantities in quantum physics
00:42:23.120 physical variables are typically discrete and so cannot undergo tiny changes instead a tiny effect
00:42:30.080 means a tiny change in the proportions that have the various discrete attributes this also raises
00:42:36.080 the issue of where the time itself is a continuous variable in this discussion I am assuming that
00:42:41.520 it is however the quantum mechanics of time is not yet fully understood and will not be until
00:42:48.240 we have a quantum theory of gravity the unification of quantum theory with the general theory of
00:42:52.720 relativity so it may turn out that things are not as simple as that one thing we can be fairly
00:42:58.160 sure of though is that in that theory different times are a special case of different universes
00:43:04.000 in other words time is an entanglement phenomenon which places all equal clock readings of correctly
00:43:10.000 prepared clocks or of any objects usable as clocks into the same history this was first understood
00:43:14.800 by physicist Don Page and William Wooters in 1983 pause their mind reflection so that's some
00:43:20.240 very interesting stuff there about the physics of time and David has spoken elsewhere about
00:43:27.280 the physics of time because the time has this very what was the time I think it was Thomas
00:43:34.560 Aquinas who said something to the effect of them I know exactly what time is until someone asks
00:43:39.600 me time has been mysterious for a long time in physics but there is an interview that David Deutsch
00:43:46.480 gave and I'll link to it in the description to this video that I think articulates quite well
00:43:54.320 what time kind of years and why isn't as mysterious sometimes as many people think
00:43:59.440 but let's not get distracted by that just for now and I'm skipping a bit and I'm skipping
00:44:06.720 two a large part about what I would still call Harry Potter universes where
00:44:14.000 David is talking about boiling some water for example and yes and this is what in the last episode
00:44:19.920 Brett Weinstein was very concerned about that sometimes these highly unlikely events indeed happen
00:44:29.040 and you know for example if you're boiling water David writes in some tiny sliver of the multiverse
00:44:35.440 the kettle transforms itself into a top hat and the water into a rabbit which then hops away
00:44:40.000 and you get neither tea nor coffee but rather a very surprise that is the history
00:44:46.000 after that transformation but there is no way of correctly explaining what was happening during it
00:44:50.400 or predicting the probabilities without referring to other parts of the multiverse and
00:44:53.680 normally larger parts with larger measures in which there was no rabbit yes and so there's no reason
00:44:59.440 to reject the multiverse just because there's this tiny tiny sliver of universes in which some
00:45:06.000 bizarre things happen and what David writes about this okay so where we have a situation where
00:45:12.800 you're boiling water to make tea throughout your entire life of course every time you boil water
00:45:20.000 to make tea one would expect nothing particularly unusual happens but David does say that well it's
00:45:26.640 consistent with the laws of existence quite possible for the kettle to turn itself into a top hat
00:45:32.560 and the water to turn itself into a rabbit which can hops away so we've got these kind of two
00:45:36.640 versions the one in which you boil water nothing unusual happens and you might tea and one in which
00:45:41.440 you end up with the rabbit on that David says and so I'm skipping a huge amount here from
00:45:49.120 this chapter from the beginning of infinity but I'll just concentrate on the section where he says
00:45:53.600 quote the rabbit history is fundamentally different from the tea history in that the latter the tea
00:45:59.840 history remains very accurately autonomous throughout the period in the rabbit history I end up with
00:46:06.720 memories that are identical to what they would be in a history in which water became a rabbit
00:46:12.320 but those are misleading memories there was no such history the history containing those memories
00:46:18.000 began only after the rabbit had formed for that matter there are also places in the multiverse
00:46:24.720 of far larger measure than that one in which only my brain was affected producing exactly those
00:46:30.880 memories in effect I had an hallucination caused by random motion of the atoms in my brain
00:46:37.520 caused their my reflection so just to emphasize this bit yes it's possible that indeed a kettle
00:46:46.800 can form itself to a top hat and water can form itself into a rabbit such that boiling tea
00:46:52.480 boiling water for tea leads to this rabbit jumping out of a top hat but as David says they're not
00:46:58.880 only is that exceedingly unlikely the tiny tiny measure of universe which that happens but
00:47:07.280 if you actually did have that memory if you actually if that seemed to have occurred to you
00:47:12.960 the better explanation according to quantum theory is that that occurred only in your brain
00:47:19.760 that there was misfiring of neurons in your brain that caused you to hallucinate that exact thing
00:47:25.840 rather than that exact thing actually happening okay so quantum theory makes sense out of those things
00:47:36.080 and David writes straight after that some philosophers make a big issue of that sort of thing
00:47:41.360 claiming that it casts doubt on the scientific status of quantum theory but of course they are
00:47:46.480 empiricists in reality misleading observations misleading memories and false interpretations
00:47:51.840 are common even in the mainstreams of history we have to work hard to avoid fooling ourselves
00:47:58.080 with them so it is not quite true that for instance there are histories in which magic appears to
00:48:02.960 work there are only histories in which magic appears to have worked but will never work again
00:48:08.320 there are histories in which I appear to have walked through a wall because all the atoms of
00:48:12.640 my body happen to resume their original courses after being deflected by atoms in the wall
00:48:17.120 but those histories began at the wall the true explanation of what happened involves many other
00:48:22.400 instances of me and it or we can roughly explain it in terms of random events at very low
00:48:27.440 probability it is a bit like winning a lottery the winner cannot properly explain what has just
00:48:33.040 happened without invoking the existence of many losers in the multiverse the losers are the other
00:48:39.440 instances of oneself skipping a little bit more and reaching the end of this chapter here
00:48:46.480 and it ends in a very poetic and eloquent way this won't be the end of the episode
00:48:52.160 but there will be the end of me reading the books I'm going to read at the final
00:48:57.040 two paragraphs of the chapter here and David writes we namely people we are channels of information
00:49:07.520 flow so are histories and so are relatively autonomous objects within histories but we
00:49:14.000 sentient beings are extremely unusual channels along which sometimes knowledge grows
00:49:20.560 this can have dramatic effects not only within a history where it can for instance have
00:49:25.440 effects that do not diminish with distance but also across the multiverse since the growth of
00:49:31.200 knowledge is a process of error correction and since there are many more ways of being wrong than
00:49:35.760 right knowledge creating entities rapidly become more alike in different histories than other
00:49:41.920 entities as far as is known knowledge creating processes are unique in both these respects
00:49:48.880 all other effects diminish with distance in space and become increasingly different across the
00:49:53.680 multiverse in the long run but that is only as far as is known here is an opportunity for some
00:50:00.480 wild speculations that could inform a science fiction story what if there is something other
00:50:05.360 than information flow that can cause coherent emergent phenomena in the multiverse
00:50:10.160 what if knowledge or something other than knowledge could emerge from that and begin to have
00:50:16.080 purposes of its own and to conform the multiverse to those purposes as we do could we communicate
00:50:22.240 with it presumably not in the usual sense of the term because that would be information flow
00:50:27.120 but perhaps the story could propose some novel analogue of communication which
00:50:32.000 like quantum interference did not involve sending messages would we be trapped in a war of mutual
00:50:37.680 extermination with such an entity or is it possible we could nevertheless have something in common
00:50:42.400 with it let us shun parochial resolutions of the issue such as a discovery that what bridges the
00:50:48.240 barrier is love or trust but let us remember that just as we are at the top rank of significance
00:50:54.160 in the great scheme of things anything else that could create explanations would be too
00:50:59.680 and there is always room at the top okay and that's the end of the chapter and there was
00:51:04.000 always room at the top is a reflection of Richard Feynman's quip but there is always room at the
00:51:10.240 bottom in other words there is a lot of space down there when you get smaller and smaller
00:51:17.280 than molecules so you can store a lot of information in small stuff and data there is reflecting
00:51:24.080 that with there is always more and more space out there as we get larger as well now David has
00:51:30.800 ended the chapter there with mention of interesting science fiction stories and so it's also the
00:51:39.040 way he began the chapter with an interesting science fiction story and I have been promising
00:51:45.200 for about four episodes that I would explain the way in which the multiverse can be tested
00:51:52.160 against other interpretations of quantum theory like any collapse model for example now I'm not
00:51:58.640 going to talk about ways in which we can test the multiverse theory against for example
00:52:05.040 things like the bermium pilot wave model as David has explained even recently
00:52:09.440 these are versions of quantum theory which really are the multiverse in heavy disguise
00:52:16.240 I might mention the bermium theory shortly but what I want to do now is to tell a story
00:52:23.120 to tell a science fiction story about how to test an experimental test of the multiverse theory
00:52:30.480 against the Copenhagen interpretation against any other interpretation that involves the collapse
00:52:38.240 of the wave function and so for that I'm going to have to change then you so here we are for the
00:52:43.680 long promised explanation of how the multiverse is testable now in previous episodes I have
00:52:50.720 actually explained certain ways in which the multiverse is experimentally testable but today on
00:52:57.280 finally going to get to David Deutsch's own experimental test of the multiverse interpretation
00:53:04.720 versus all those other kinds of interpretations of quantum theory namely the ones that involve so
00:53:10.240 called collapse of the wave function so collapse models now the way in which I'm going to explain
00:53:16.800 this experiment is not by simply reading David's papers that he's written on this or even going
00:53:23.120 to some other popular accounts of it but rather I'm going to try and turn it into a story
00:53:28.240 and the reason for doing it this way a reason for telling a story the story of the experiment
00:53:34.880 is the experiment isn't practically feasible right now but it will be one day
00:53:41.040 so it's kind of like how the Higgs boson this particle that gives other particles mass
00:53:47.760 was postulated long before there was an actual practical way of testing it took the
00:53:53.200 large Hadron Collider you know a piece of scientific apparatus much larger than anything else that
00:53:58.560 had gone before it it took decades before the hypothesis of the Higgs boson could be tested by
00:54:04.080 experiment or rather before the theory of the Higgs boson could be tested by experiment namely
00:54:09.360 the large Hadron Collider smashing particles together and seeing what came out and seeing if we
00:54:14.080 could actually observe the Higgs boson of course as perperians what we say is that we weren't
00:54:19.680 confirming the existence of the Higgs boson we were refuting all the other ideas about what
00:54:24.800 those observations could mean namely if the Higgs boson was some other kind of particle so every
00:54:30.640 other theory about what was going on in those experiments was refuted but the Higgs boson
00:54:36.160 explanation of the observations was not refuted and so therefore we say that those experiments
00:54:41.280 from the large Hadron Collider did indeed reveal the existence of the Higgs boson all right so now
00:54:46.960 it's story time this is a science fiction story so perhaps sit back get yourself a nice cup of tea
00:54:58.480 and enjoy being transported to the future so picture it's the year 2075 and though quantum
00:55:06.720 computers are now carrying the pockets of most people David Deutscher's proposed test of
00:55:12.400 Everrettian quantum theory against other so-called collapse models has yet to be performed
00:55:19.120 many artificial general intelligences actually now populate the earth and while many silicans as the
00:55:25.680 new general intelligences are happy to be called choose to house their minds within bodies that
00:55:31.120 closely resemble those of typical humans others choose to take the form of cars or aircraft
00:55:38.080 some few even choose bodies that double as space-faring vehicles because without the need
00:55:43.200 oxygen or indeed air of any kind they can routinely explore the darker reaches of the solar system
00:55:50.000 just for fun some of these intelligent spacecraft are very large indeed as they may carry huge
00:55:56.720 payloads of batteries and some also choose to be employed as cargo vessels shipping resources
00:56:02.320 between earth and other bodies in the solar system now one of these space silicans and the hero
00:56:07.840 of our story is called parlox cubite parlox has what in the year 2020 would be regarded as a
00:56:16.240 very unusual body for a person he has the shape of a very long about a hundred meters and very
00:56:22.880 wide say about 50 meters box which is not very deep something about five meters deep so this is
00:56:28.800 his body his body is a box this is useful for carrying cargo only a small portion of his body
00:56:35.840 houses batteries and a landing gear and rocket fuel for landing and takeoff parlox can land in
00:56:41.280 any number of configurations and generally takes off in such a way as to minimize his cross-sectional
00:56:46.080 area and reduce air resistance on low gravity moons he's an explorer this parlox he likes to move
00:56:51.520 between places in the solar system that no one else has been to before and so this is why he's
00:56:56.160 chosen the body that he has now on a particular day somewhere in 2075 parlox is traveling from
00:57:04.480 earth to Jupiter's moon Europa it has long been known that the radiation saturating the surface
00:57:10.240 of Europa from Jupiter is too intense for any regular human to endure so despite many probes over
00:57:15.920 the years visiting the moon few people and no manned missions have ever landed there parlox is a
00:57:22.800 physical chemist by training and wants to investigate the ocean beneath the ice on the surface
00:57:27.440 for signs of life so far no other missions have found any evidence at all the journey to Europa is
00:57:34.080 two months long and though he could enter a kind of hibernation state most silicon's are found
00:57:39.840 for reasons yet to be known that the hibernation state tends to cause uncomfortable nightmares
00:57:45.520 about three days in and terrible dizziness upon waking for this reason on long journeys like
00:57:51.440 this parlox chooses the best known sleep wake sleep or wake cycle sleep seven hours wake seven
00:57:58.400 hours sleep nine hours wake nine hours repeat he also has a list of tasks he set himself to
00:58:05.520 keep himself occupied one item on the list that he's particularly excited about refers to a message
00:58:10.880 in his ongoing correspondence with the now 122 year old professor David Deutsch parlox asked whether
00:58:18.960 he might be able to conduct an adapted version of Deutsch's test set out in section eight of
00:58:23.920 his 1985 paper quantum theory as a universal physical theory as published in the international
00:58:30.080 journal of theoretical physics volume 24 David and parlox plan to co-author the paper in which
00:58:36.480 the results will be published and finally perhaps putting to rest what they regard as almost 150
00:58:42.480 years worth of nonsense in the foundations of quantum theory parlox's huge body ears right now
00:58:49.600 empty and an almost perfect vacuum isolated from any other matter as it travels through the
00:58:55.360 emptiness's space but inside his cavernous body is one of the most perfect mark zender interferometers
00:59:02.320 ever to have been created the harpsil with mirrors near perfect the laser perfectly able to
00:59:07.840 attenuate the beam down to just one photon each microsecond second or even hour if you like
00:59:13.040 the detectors the most sensitive ever created there are two regular mirrors in the experiment
00:59:19.760 regular except for one thing these mirrors are directly wired to parlox's mind so I just say
00:59:27.760 that again these mirrors that are inside parlox's body are directly wired to his mind
00:59:34.480 much like the retinas in our eye are directly wired via the optic nerve to our brains and our
00:59:40.080 minds so parlox has a very special sense organ parlox can detect the slightest vibration of these
00:59:49.280 mirrors due to a collision with something as small as a single photon parlox has a mind running on
00:59:56.720 a brain with switching speeds as fast in the speed of light as all AGI in the year 2075 do
1:00:02.560 and so he is able to record and transmit data at this speed now I've got a schematic here a
1:00:09.360 picture of the internal workings of parlox's sense organ that is the mirror set up and as we can
1:00:16.480 see the inner workings of this particular organ if you like in parlox's brain are very similar
1:00:23.440 to the mark zender interferometer so we've got some source of photons the harpsil the mirror
1:00:30.800 where the beam will be split into an up part and a down part that's the U and the D the regular mirror
1:00:37.920 there is pair is parlox's sense organ it connects that regular mirror via some cable some wire
1:00:44.640 some nerve of the parlox's mind a similar thing with the other regular mirror that is on the
1:00:51.040 down part and then as usual in the mark zender interferometer we've got a couple of detectors there
1:00:56.480 detectors one and two now parlox has carefully set up the lengths of the U the up path and the D
1:01:03.680 down path according to collapse theories like the Copenhagen interpretation indeed according to
1:01:10.560 any interpretation that is not literal quantum theory saying all possibilities really do exist
1:01:16.400 namely a multiverse when a photon is emitted at the source it makes no real sense to ask which
1:01:22.960 of the paths the photon takes it simply has a 50% chance of going along the U path and a 50%
1:01:29.440 chance of going along the D path if no one observes which of these paths it goes along
1:01:34.800 then the photon will be detected with 100% probability at detector one and zero percent probability
1:01:41.280 at detector two this is because of how parlox has set up the experiment namely by ensuring that
1:01:46.720 the path length of U and D is slightly different but the details do not matter and I've mentioned
1:01:51.040 this in an earlier episode as well about the details of how the mark zender interferometer works
1:01:57.120 what the collapse interpretation says as do other interpretations is that some sort of interference
1:02:03.200 effect has happened and that when the photon is finally detected at detector one all the possibilities
1:02:08.560 have collapsed into one but what the collapse theory also says is that if anyone were to observe
1:02:15.760 the photon mid-flyed for example if they knew it was traveling along the D path and not the U
1:02:20.480 path then the interference effect would be destroyed and we would have 50% of the photons going
1:02:25.920 to detect a one and 50% to detect a two in other words there is a special kind of physics of
1:02:31.040 observation in quantum theory observation has a special effect in the world so this is on the
1:02:36.640 Copenhagen or any so-called collapse theory observation has a special role in the world it has
1:02:42.960 special physics anyone who says that the way function collapses or wonders about what happens
1:02:48.240 during collapse or why it collapses and so on these people believe in alternatives to the multiverse
1:02:54.320 but on the other hand proponents of the ever-at-way of understanding quantum theory the
1:02:59.440 realistic way of understanding quantum theory the literal reading of the equations of quantum theory
1:03:04.160 is to say that no such collapse happens observation has no special role observation does not
1:03:11.280 cause the collapse of the wave function there is nothing special about observations on this view
1:03:16.080 the so-called measurement problem is that sometimes called is solved it dissolves away by saying
1:03:21.200 there is no special physics of measurement so when it comes to the inner workings of parloxes
1:03:26.560 braying its sense organs going on here the ever-at-understanding of this is that both possibilities
1:03:33.280 happen both the up and the down paths are followed and this in fact explains why interference
1:03:39.520 effects occur the photon is fired from the source the photon is in fact a multiverse
1:03:44.720 object when the photon encounters the half silver mirror all the universes in which the experiment
1:03:49.440 occurs differentiate into two groups one in which the photon takes the u-path and another group
1:03:56.000 in which the photon takes the d-path this is the only difference between the two groups of universes
1:04:01.280 these two universes then recombine at the second half silver mirror just prior to the detectors
1:04:07.360 and it is the literal collision between these two photons the photons at the u and the d-path
1:04:12.080 that caused the new recombine photon to set up the detector at detector one but not detector two
1:04:18.000 now the key thing here for the year 2075 and for parlox and what we're now able to do
1:04:25.040 in the distant future is that parlox is in fact able to sense the collision of the photon
1:04:31.680 at either of the regular mirrors because he has a sense organ so he is able to observe interference
1:04:38.880 going on prior to it happening so parlox's sense organs are part of the experiment his sense
1:04:45.840 organs are those mirrors those regular mirrors he can detect if photons are striking those mirrors
1:04:53.280 and so he is an observer of the experiment while it's going on hit the two impossible to do
1:04:59.120 because we humans don't have such sense organs but an artificial general intelligence in the future
1:05:04.320 could have such a sense organ could build themselves such a sense organ and perform this experiment
1:05:10.320 according to the collapse interpretation this should cause the interference effect to be lost
1:05:17.280 because it has been observed according to those interpretations i all other interpretations
1:05:22.800 besides the multiverse observation plays a key role in physics it causes the collapse of the wave
1:05:27.840 function at least a dissupposed to so in this view if we repeat the experiment we should see
1:05:33.120 half the photons to be detected one and half the two no matter what if parlox is sensing
1:05:38.480 that is to say observing them with his sense organs the regular mirrors and if indeed the interference
1:05:45.440 files to occur during this observation experiment during this interference experiment
1:05:51.120 and parlox is observing it then we have refuted the multiverse theory this is the sense in which
1:05:58.560 the multiverse is testable we can refute we can test we experimentally test and falsify the multiverse
1:06:05.600 theory of course we have no real alternative but according to the multiverse account of things
1:06:11.680 no collapse happens so long as parlox keeps the information about which mirror he has detected a
1:06:17.120 collision at to himself here's what goes on according to literal quantum theory i according to
1:06:23.120 the multiverse the photon at the first half silver mirror causes the differentiation of the
1:06:29.680 universe into two groups in half the universe's the photon travels the d path and parlox in the d
1:06:36.880 universe detects the collision with the photon in the other half of the universe's parlox detects
1:06:43.520 the photons having traveled the u-path parlox himself actually splits into two separate versions
1:06:51.600 in either case parlox u or parlox d in whichever universe he can record and transmit
1:06:59.600 back to David an intermediate result and say i can testify that i have observed a photon
1:07:05.920 traveling along one and only one path it must be the same message in either case now the distances
1:07:13.040 d and u are long and it takes light some time to traverse this path so parlox does indeed have
1:07:18.960 time to do all this because he's got a fast brain remember but very soon after he sends that
1:07:24.880 message the message that says i have detected the photon striking one of my mirrors and only one
1:07:30.400 of my mirrors he then sends another message and he repeats the experiment again and again
1:07:36.880 as good scientists do sending message after message back to David who's part of the experiment
1:07:42.800 if the messages went something like this i have detected the photon at one and only one mirror
1:07:48.480 the next message comes i have detected the photon at the tep2 and then i have detected
1:07:55.760 the photon at one and only one mirror i have detected the photon at tep1 i have detected
1:08:02.960 the photon at one and only one mirror i have detected the photon at the tep2 and so on
1:08:08.800 in other words, roughly half the time detector one is activated and half the time detector two
1:08:15.360 is, because the photon only ever takes one path, either the u or the d-path, it does not
1:08:20.960 take both paths simultaneously. If this was to happen, if this was to happen, the multiverse
1:08:26.840 is refuted, however, if the message was to run this way, I have detected the photon at
1:08:34.480 one and only one mirror. Time delay, I have detected the photon at detected two, and then
1:08:42.200 I have to detect the photon at one and only one mirror, time delay, I have detected
1:08:47.320 the photon at detected two, etcetera, it keeps on detecting it at detected two, then interference
1:08:54.600 has happened. Despite the fact the photon was observed that only ever one of the mirrors.
1:09:01.440 What this means is that the active observing the photon has not collapsed to the wave
1:09:06.480 function, and though the photon was detected at only one mirror, something travelled along
1:09:10.760 the other path, in another universe, shoving aside the photon each time, and this collision
1:09:16.080 forced the recombined photon to travel always into detected two. Now it is crucially important
1:09:23.240 that Parlogs tells no one which mirror he observed the photon struck, because this ruins
1:09:29.120 the experiment. It ruins the experiment because once he says I detect the photon having
1:09:33.800 struck only one mirror, and that is the mirror corresponding to the u-path. This means that
1:09:39.040 the universe have differentiated still further, and cannot come together again to interfere,
1:09:44.680 they cannot become fungible once more. The interference can happen if, and only if, the
1:09:50.440 only thing that is different between them is the path of this single photon. If other
1:09:56.000 things start to change, like for example Parlogs sends David a message that the D-path
1:10:01.400 was the one travelled, then David also knows in which universe he and Parlogs are in, and
1:10:06.480 that is a difference in that universe outside the experiment. This is called decoherence,
1:10:11.520 by the way, decoherence is where information is leaked out of the experiment into the world
1:10:16.480 differentiating the universes. Moreover, the message itself will carry different information
1:10:22.480 in the two universes, making them quite different, and increasingly different as the
1:10:26.520 energy of the message, as it goes, as it travels back to the earth, collides with objects
1:10:31.680 in the solar system. We need to keep the differences only, and exclusively, inside of
1:10:37.240 Parlogs' mind, and effectively this entire apparatus is in Parlogs' mind, or brain, shielded
1:10:43.800 as it were from the rest of physical reality. This might seem awfully contrived, this
1:10:49.520 might seem bizarre. What on earth are we doing in the year 2075? Why do I have artificial
1:10:54.240 general intelligence? Don't blame the multiverse theory. This bizarre way of testing
1:11:00.600 the multiverse is not the fault of the multiverse theory. It's the fault of the so-called
1:11:06.440 mainstream Copenhagen interpretations, or any of the collapse models. They're the
1:11:11.880 weed theory that requires a weird test to refute. That's all. It is those theories that
1:11:19.280 says there is a special role for observers, and so we need to be able to test this special
1:11:24.080 role of observers. It is observers on that account, on that Copenhagen account, on the
1:11:30.480 collapse models account. It is those theories that say there is a special role for observers.
1:11:39.520 That special role is that the observers collapse the wave function. That's what all other
1:11:44.680 interpretations say. That is the spooky and strange claim. So to rule that out, that's
1:11:51.200 why we need this elaborate method inside of a mind to test the claim that observers
1:11:55.920 or minds or something like that is causing the collapse, the vanishing of all the possibilities
1:12:00.440 except for one. If we can rule out this single universe model by having interference between
1:12:06.280 two universes occur within a single mind, then we refute the observer dependence of quantum
1:12:11.280 theory. With the many worlds idea of Everett and more precisely Deutsch, who replaced the
1:12:16.520 concept that Everett had, a branching of a small number of universes into a larger and larger
1:12:22.520 number, and instead David said, well, that's not quite right. It's not that we start off
1:12:27.240 with a small number, and that number gets greater and greater and greater over time as quantum
1:12:32.480 phenomena occur. But rather he said that the number of universes there, but the number
1:12:38.600 of universes that exist all the way back to the beginning of time, a constant number
1:12:43.480 and began fungible, but then differentiate when the possibilities arise. We conclude
1:12:48.600 that the single universe theory and collapse models can be refuted by this means. The
1:12:54.120 only known explanation is that the multiverse did split or differentiate into two different
1:12:59.240 groups, a U-group and a D-group, and these universes then interfered with each other in such
1:13:04.640 a way that the photon is only of the detected at, detected two and never detected one, despite
1:13:10.840 the fact it was observed by parlocks at only one of the two mirrors. And this was possible
1:13:16.640 because parlocks really did split into two versions of himself, different only to the extent
1:13:21.480 of observing a single photon along the D-path or along the U-path. Now, what this might
1:13:26.400 be like to split into two copies, they're no longer fungible, and then to come back together
1:13:31.800 to have these kind of sense organs is anyone's guess at all, but I guess he was having
1:13:36.680 fun. After all, he did know that he was going to be authoring a co-authoring a paper
1:13:40.120 with David Doge about the fundamentals physics, so that must have been pretty exciting.
1:13:46.120 Once he experimenters over, it makes no sense to ask parlocks which mirror did you actually
1:13:51.240 detect the photon at? Was it the mirror at the D-path or the mirror along the U-path? Parlocks
1:13:59.280 won't be able to say, because the two versions of parlocks, and indeed the whole two
1:14:03.680 groups of universes have recombined at the second half silver mirror, parlocks simply
1:14:08.840 cannot remember. Because he split into two different copies, one of whom experienced
1:14:15.920 you and one of whom experienced D, but he only recalls ever having experienced one. This
1:14:22.160 is where language kind of breaks down. He both experienced both and one simultaneously.
1:14:28.680 Very strange. So, language somewhat fails to capture what is going on here, but the truth
1:14:33.880 is he was both copies for a very brief amount of time. And again, whether this felt
1:14:39.560 like something special or nothing particularly special, we may be able to interrogate him
1:14:44.200 about that. But he'll never be able to tell us which mirror he detected the photon at.
1:14:51.880 Once he becomes fungible again, once the two versions of him combined together to become
1:14:56.920 a single version of parlocks once more. So, he will in fact be the first earthling
1:15:02.280 ever to have experienced this sensation of knowing he was in two universes at the same
1:15:06.320 time, and then becoming one version of himself in one universe again. Now, that's if
1:15:13.600 it all works out as predicted by the multiverse. But what if he does not have this experience
1:15:18.160 of being in and conscious of two different non-fungible universes simultaneously? Well,
1:15:22.920 then the whole experiment would refute the multiverse because observation apparently would
1:15:27.640 collapse away function, or better to say the multiverse itself is simply refuted. The point
1:15:33.320 is, if the experiment works as predicted, there is no way of explaining any of it by
1:15:36.880 recourse to a collapse model where all the universes but one sees to exist. So, if indeed
1:15:42.000 the interference fails to happen as predicted, then parlocks is experiment, David Deutsch's
1:15:47.320 experiment, has roundly refuted the multiverse. Quantum theory would then have a hugely
1:15:53.520 open problem about how observation works and why it is so fundamental to the nature
1:15:58.120 of the universe. We would need to develop a new physics of observation and measurement.
1:16:02.960 And physics would become, in part, fundamental physics would become in part about us, about
1:16:07.960 people and how it is that our choice to observe stuff or not can cause the majority of
1:16:13.040 reality to vanish in an act of performing a scientific experiment. When we choose to perform
1:16:19.600 particular experiment, we're causing the collapse of the wave function, the collapse
1:16:22.440 of all these other realities that come to bear causing the result of the experiment to
1:16:26.800 be the way it is. Whereas the multiverse just says all those realities really do continue
1:16:31.600 to exist. Whatever the case, the multiverse is eminently testable by this technique
1:16:36.640 and in principle, falsifiable. So, that's that. After many months of prominence, I
1:16:42.880 hope this satisfies some of you on the most contentious point when it comes to the multiverse.
1:16:50.000 Well, perhaps not the most contentious point. One of the most contentious points. Namely,
1:16:54.240 the multiverse is a testable theory from a number of different angles. There are experiments
1:17:00.400 possible and the strange experiment here, again, is not the fault of the multiverse. It's
1:17:05.440 the fault of the collapse models that propose observation is a fundamental thing that affects
1:17:09.280 reality. So, we need an experiment that could possibly refute this idea. And David's version
1:17:15.480 of this is different to the one that I've just told. Mine is based entirely on his. Of
1:17:20.520 course, here is a completely mine, but I thought that because we'd already explained the
1:17:25.320 mark's ending interferometer, I wanted to explain that way of doing this experiment.
1:17:30.280 Now, the way that David does it is via looking at this thing called the Stern-Goulash experiment,
1:17:35.840 the pronunciation may be wrong there, and a property of subatomic particles called spin.
1:17:42.600 And so, rather than attempting to explain all of that, I've stuck with what I hope we're
1:17:48.360 already familiar with if you're being bearing with me through this multiverse series. And
1:17:53.520 on that, this video doesn't quite finish the multiverse series, but for now it does.
1:18:00.240 I've a couple more things to say about the multiverse, but we're going to save those for
1:18:03.360 a more distant episode. For now, I wish to move on to the next chapter, chapter 12, a
1:18:08.640 physicist's history of philosophy. And that should be a lot of fun because bizarre as some
1:18:15.360 of the things that we've been talking about during this series have been, like the claim,
1:18:21.440 for example, that your observations can cause vast parts of physical reality to cease
1:18:26.480 to exist. The reason why people, including very smart people, very smart physicists, might
1:18:34.000 come to endorse or insist on such ideas, or do very bizarre things like reject the multiverse,
1:18:40.560 it's not because of the science, but it's because of their philosophy, bad philosophy.
1:18:47.320 And an overview of bad philosophy by David Deutsch is just the remedy for undoing poor thinking
1:18:52.720 on this point. And it will help us to understand why quantum theory in particular has a special
1:19:00.960 place in the hearts of many, many philosophers, because of this bad philosophy. So the scientific
1:19:06.720 community has sort of treated quantum theory in a way that's somewhat different to the way it
1:19:12.400 treats any other scientific theory. But we'll get on to that. We'll get on to why bad philosophy
1:19:18.000 has come to taint our understanding of quantum theory and hampered progress in quantum theory
1:19:23.520 this time. Until then, bye-bye.